Defective hematopoiesis and hepatic steatosis in mice with combined deficiencies of the genes encoding Fancc and Cu/Zn superoxide dismutase

Abstract

IntroductionFanconi anemia (FA) is an autosomal recessive disease of childhood characterized by progressive pancytopenia, various developmental abnormalities, and a predisposition to acute myeloid leukemia. 1 Most individuals with FA, however, succumb to the complications of aplastic anemia. 2 FA cells demonstrate increased sensitivity to DNA cross-linking agents such as mitomycin C (MMC), diepoxybutane, and cisplatin, 2,3 a feature that serves as the basis for an important diagnostic test. FA cells treated with these cross-linking agents show a striking increase in double-strand DNA breaks and inhibited growth with cell cycle arrest in G 2 . 2 To date at least 7 potential FA genes have been indicated by complementation studies, and most of these genes, FANCA, FANCC, FANCD2, FANCE, FANCF, and FANCG, whose mutations account for 6 of the complementation groups, have now been characterized. [4][5][6][7][8][9][10] Despite the variety of genes involved in this disorder, mutations in FANCA and FANCC account for approximately 80% of all patients with FA. 11 Murine Fancc, being highly similar to the human ortholog, is able to complement human cells deficient in FANCC, restoring MMC resistance. 12 Fancc-deficient mouse strains were generated through gene targeting. Both had similar phenotypes, 13,14 demonstrating compromised gametogenesis, and an increase in the number of chromosomal aberrations, both spontaneously and after exposure to MMC. However, the targeted lines recapitulated neither the developmental nor the hematologic defects typical of human FA. 13,14 The reason for this interspecies discordance is unknown, but it has limited the utility of the mutant mice as potential models of FA.A number of hypotheses regarding the nature of the primary defect in FA have been suggested, including the proposal that FA proteins constitute a DNA damage recognition and signaling pathway, whose impairment is manifested by chromosomal instability and increased sensitivity to interstrand DNA cross-linking agents. 15 Although a reduced ability to process DNA cross-links is clearly evident, it has also been proposed that an abnormal reduction of MMC in FA cells leads to the production of reactive species that in turn generate cross-links and other types of oxidative lesions. 16 Thus, FA might also result, at least in part, from an abnormal regulation of cell redox state or of the cellular response to oxidative stress or both. In support of this notion, addition of Cu/Zn superoxide dimutase (SOD) to the culture medium of FA cells was reported to attenuate chromosomal breakage as well as MMC cytotoxicity, 16 an effect also observed in FA cells overexpressing thioredoxin. 17 In keeping with an inability to regulate either production, or the consequences of reactive oxygen species (ROS), some FA cells were shown to be hypersensitive to oxygen. 16,18 Thus, cells grew slowly at elevated oxygen levels (eg, 35%) and For personal use only. on May 9, 2018. by guest www.bloodjournal.org From tended to arrest at G 2 , whereas at low oxygen conc...

Constitutive Activation of Caspase-3 and Poly ADP Ribose Polymerase Cleavage in Fanconi Anemia Cells

“…Data obtained from mouse models provided strong genetic evidence that FANCC−/− cells are hypersensitive to endogenously generated oxidants, although it was unknown whether the molecular mechanism responsible for this hypersensitivity was due to altered redox signaling (40,41). In turn, our data confirm that ROS are playing a role in FA cells and that caspase-3/PARP enzymes are activated along with MAPKs without exposure of FA cells to exogenous damaging factors.…”

Inflammatory ROS promote and cooperate with the Fanconi anemia mutation for hematopoietic senescence

“…The FA proteins are thus believed to play important roles in the maintenance of hematopoiesis. Consistent with the observations that cells derived from FA patients are intolerant of oxidative stress, it has been reported that FA proteins, particularly the complementation group C (FANCC) protein, play a crucial role in oxidative-stress signaling in a variety of cell types including hematopoietic cells (Kruyt et al, 1998;Cumming et al, 2001;Hadjur et al, 2001;Futaki et al, 2002;Park et al, 2004;Saadatzadeh et al, 2004;Pagano et al, 2005). More recently, cytokine hypersensitivity of FA hematopoietic cells to apoptotic cues has also been proposed as a major factor in the pathogenesis of BM failure in three FA mouse models…”

Acquired FANCA dysfunction and cytogenetic instability in adult acute myelogenous leukemia

“…Mutant cells exhibit spontaneous chromosomal breakage 38 and increased sensitivity to the development of cytogenetic anomalies on in vitro treatment with cross-linking agents 39 such as MMC 40 and DEB. 41 Additional functions for FA proteins have also been described, including modulation of cytokine-mediated signaling, [42][43][44][45][46][47][48][49][50] responsiveness to oxidative stress, [51][52][53][54][55][56][57] and chromatin remodeling. 58 Moreover, at least 2 members of the FA genes (FANCC and FANCD2) are multifunctional.…”